Fossilized Gastropod Internal Mold
Indeterminate gastropod stepped-spire; cf. Viviparus species or similar globose snail • Body fossil (internal mold/steinkern), Invertebrate
Geological Period
Likely Cretaceous to Neogene
Estimated Age
Approx. 23 to 145 million years
Preservation Type
Internal mold (steinkern) formed by lithification of sediment inside the shell, followed by the dissolution of the original aragonite/calcite shell.
Condition Assessment
Good; the specimen is mostly complete and retains clear whorl definition, though surface details (ornamentation) are lost because the outer shell is absent.
Taxonomic Classification
Phylum: Mollusca, Class: Gastropoda, Order: Likely Archaeogastropoda or Neogastropoda
Morphological Description
Specimen exhibits a low-conical, dextral (right-handed) spiral coiling. It features a visible spire with distinct whorls separated by deep sutures. The surface is relatively smooth due to being an internal mold, showing the internal cavity geometry of the original shell.
Rock Matrix
Calcareous mudstone or fine-grained limestone; the specimen itself is composed of hardened sedimentary infill.
Formation & Location
Common in marine and freshwater sedimentary deposits worldwide; specifically consistent with the Glen Rose Formation (USA) or European Jurassic/Cretaceous chalks.
Size & Dimensions
Approximately 2-4 cm in diameter; consistent with average adult sizes for common prehistoric pond or shallow marine snails.
Value & Rarity
Estimated Market Value
$5.00 - $15.00 USD
Auction Estimate
$10.00 - $20.00 USD (typically sold in bulk lots)
Rarity Assessment
Common; gastropod molds are among the most frequently found invertebrate fossils in sedimentary basins.
Scientific Significance
Provides data on paleoenvironmental conditions (marine vs. freshwater) and helps in the stratigraphic dating of the sediment layer in which it was found.
Preparation Recommendations
No further mechanical preparation needed. Should be kept in a dry environment and can be stabilized with a very dilute B-72 coating if the matrix is friable.
Notable Features
The specimen is a classic example of a 'steinkern,' clearly demonstrating how sediment fills an organism's void to create a geological record after the organic material decays.